In order to localize the parts of brain which participate in processing visual information, we have measured rates of local cerebral glucose utilization in monkeys during the performance of a task cued by specific visual stimuli. A surgical preparation resulting in one hemisphere's being totally deprived of visual input while the other is normally sensitive to the visual cues has permitted the mapping of those cortical areas beyond the primary visual cortex which are involved in processing visual information. We now wish to learn of the functional development of this extended cortical pathway and so are continuing these same studies in the monkey at various postnatal ages. Although the project began with its focus on mapping the visually responsive cortical areas, the experiments also permit an analysis of the sensory-motor system. Normal control monkeys with their visual pathways intact responded to the visual cues by pressing a lever with one hand. This invoked an asymmetrical pattern of local glucose utilization in brain involving a wide expanse of cortical and sub-cortical structures. An analysis of the pattern of asymmetry provides new information with respect to the localization sensory-motor function. The data obtained to date indicate that a much larger portion of brain regions are unilaterally activated on unimanual activity than has been appreciated previously.